1. Field of the Invention
The present invention relates to an intake air flow rate control device for controlling an intake air flow rate for an internal combustion engine by operating a throttle valve driven by a motor.
2. Discussion of Background
According to a conventional technique, in a combustion engine equipped in a conventional vehicle, a throttle valve located in an intake air passage is connected to an accelerator pedal by a mechanical means such as a linkage mechanism and a cable, and an opening degree of the throttle valve is operated in association with an amount of stepping the accelerator pedal, whereby the intake air flow rate is controlled. By a control of the intake air flow rate by the mechanical means, the amount of stepping the accelerator pedal and the opening degree of the throttle valve are univocally determined, a control of the throttle valve using elements other than the amount of stepping the accelerator pedal is difficult, and a degree of freedom of a relationship between positions of the accelerator pedal and the throttle valve in the vehicle is limited.
Therefore, in recent years, an intake air flow rate controlling device of an electronic control type is popularly used, wherein the controlling device makes a throttle valve open and close by a driving force of a motor, an amount of stepping an accelerator pedal is electrically detected, and the throttle valve is driven by the motor based on thus detected amount. The intake air flow rate controlling device of the electronic control type controls the motor by receiving various signals other than the amount of stepping the accelerator pedal to enable an operation of opening and closing the throttle valve, and various running conditions are used as inputs into the controlling device to control the throttle valve.
For example, in a gasoline engine of a direct cylinder injection type, an air fuel ratio is widely changed from a theoretical air fuel ratio to an air fuel ratio for lean burn. However, there is a large difference between torques generated by an internal combustion engine under the theoretical air fuel ratio and the air fuel ratio for lean burn when an opening degree of the throttle valve is the same. At a time when the air fuel ratio for lean burn is changed to the theoretical air fuel ratio, it is necessary to correct the intake air flow rate by controlling the opening degree of the throttle regardless of the amount of stepping the accelerator pedal in order to restrict a variation of the torques, whereby the electronically controlled intake air flow rate controlling device is indispensable to such an internal combustion engine.
The electronically controlled intake air flow rate controlling device obtains a present opening degree of the throttle valve by receiving a value detected by a throttle valve opening degree detecting sensor located in the throttle valve, operates a target opening degree of the throttle valve with respect to the present opening degree, and drives the motor. However, an error in the detection and so on make a difference between the detected value by the throttle valve opening degree detecting sensor and an actual throttle valve opening degree, and the difference varies depending on a change of an ambient temperature and so on. For example, when the throttle valve is controlled to be completely closed, the throttle valve is actually in a completely closing position, the detected value of the throttle valve opening degree detecting sensor is not in conformity with the completely closing position. Therefore, the controlling device continuously drives the motor and increases the driving current to completely close the throttle valve, whereby there is a possibility that the motor and/or a motor driving circuit is burned out.
In order to previously avoid such troubles, in the conventional intake air flow rate controlling device of the electronic control type, the completely closing position of the throttle valve is learned from the detected value by the throttle valve opening degree detecting sensor, and a lower limit value of the target throttle valve opening degree is used as the learned value of the completely closing position. However, the learned value still has an error. Further, when the detected value from the sensor of the throttle valve opening degree is changed by a variation and so on of an ambient temperature, a difference may occur between the learned value and the detected value, whereby it was impossible to completely prevent the motor and the motor driving circuit from burning out. Further, a problem similar to those described may occur at time of completely opening the throttle valve besides the time of completely closing the throttle.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide an intake air flow rate controlling device of an electronically control type, which is not troubled even in case that a difference occurs between a detected value from a throttle opening degree sensor and an actual position of a throttle valve when the throttle valve is completely closing or completely opening.
According to the first aspect of the present invention, there is provided an intake air flow rate controlling device comprising: a throttle valve located in an intake air passage of a combustion engine; a motor controlling an intake air flow rate by operating an opening degree of the throttle valve; a motor driving means driving the motor; a throttle valve opening degree detecting sensor; a target opening degree setting means operating a target throttle valve opening degree, setting the opening degree of the throttle valve, and outputting the target throttle value opening degree as a target position signal to the motor driving means; a throttle valve completely closing position learning means learning a completely closing position of the throttle valve from a completely closing position signal from the throttle valve opening degree detecting sensor; and a throttle valve completely closing position detecting and correcting means detecting a stop of an operation of the combustion engine, operating the throttle valve to be in a completely closing position, detecting the completely closing position from the completely closing position signal from the throttle opening degree sensor, and correcting the target position signal, for a completely closing state, outputted from the target opening degree setting means by shifting the target position signal on a side of opening the throttle valve by a predetermined amount.
According to the second aspect of the present invention, there is provided the intake air flow rate controlling device, wherein the completely closing position detecting and correcting means detects the completely closing position and corrects the completely closing position learning value, outputted from the throttle valve completely closing position learning means.
According to a third aspect of the present invention, there is provided the intake air flow rate controlling device, wherein the completely closing position detecting and correcting means detects the completely closing position and corrects both of the target position signal for the completely closing state, outputted from the target opening degree setting means and a completely closing position learning value, outputted from the throttle valve completely closing position learning means.
According to a fourth aspect of the present invention, there is provided an intake air flow rate controlling means comprising: a throttle valve located in an intake air passage of a combustion engine; a motor controlling an intake air flow rate by operating an opening degree of the throttle valve; a motor driving means driving the motor; a throttle opening degree sensor detecting an opening degree of the throttle valve; a target opening degree setting means operating a target throttle opening degree, setting the opening degree of the throttle valve, and outputting the opening degree to the motor driving means as a target position signal; a throttle completely opening position learning means learning a completely opening position of the throttle valve from a completely opening position signal from the throttle opening degree sensor; and
a throttle completely opening position detecting and correcting means detecting a stop of an operation of the combustion engine, controlling the throttle valve to be in a completely opening position, detecting the completely opening position by the completely opening position signal from the throttle opening degree sensor, and correcting the target position signal outputted from the target opening degree setting means in a completely opening state by shifting the target position signal on a side of closing the throttle valve from the completely opening position signal by a predetermined amount.
According to a fifth aspect of the present invention, there is provided the intake air flow rate controlling means, wherein the completely opening position detecting and correcting means detects the completely opening position and corrects a completely opening position learning value, outputted from the throttle valve completely opening position learning means.
According to a sixth aspect of the present invention, there is provided the intake air flow rate controlling device, wherein the completely opening position detecting and correcting means detects the completely opening position and corrects both of the target position signal outputted from the target opening degree setting means for the completely opening state and a completely opening position learning value outputted from the throttle valve completely opening position learning means.